BACKGROUND: Adolescent obesity has a high risk of developing into adult obesity and may cause many physical and psychological problems. The purpose of this study was to investigate familial environment and psychosocial factors of adolescent obesity. METHODS: A total of 1,153 students from one middle school located in suburban area were chosen as subjects. In this study, the obese group was defined to have an obesity index higher than 85 pecentile, compared to the normal weight group which ranged between 25 and 75 percentile. The questionnaires included items on familial environment and psychosocial factors, their parents' BMI, physical activity, self esteem inventory, depression self rating scale, and FACES III (family cohesion and adaptability scale III). RESULTS: Maternal BMI of the obese group was significantly higher than that of the normal weight group. The mean self esteem score of the obese group was significantly lower than that of the normal weight group. Depression self-rating score of the female obese group was significantly higher than that of the normal weight group. There was no difference in family functioning between the obese group and the normal weight group. CONCLUSION: In multivariate analysis, there were significant correlations among adolescent obesity and higher maternal BMI and lower self-esteem. It will be necessary to evaluate and support the psychosocial factors in the management of adolescent obesity.